Liquid scintillation counters are mainly used for measuring low energy beta radiation emitting samples, which are of, for example, biological or medical interest. The conventional liquid scintillation counters are designed to count samples which are in the sample vials with the scintillation liquid. The volume of the sample vial is typically 6 or 20 milliliters. The sample vials are placed into sample racks, which have separate compartments for individual sample vials. The sample racks are placed on the conveyor of the automatic sample changer system of the counter.
Because the above mentioned liquid scintillation counter is designed to count vials whose volume is up to 20 milliliters, serious difficulties are encountered when the sample volume is a only few hundred microliters or less. Typically, these kind of samples are prepared in small vials, which are inserted into normal vials. In addition, the handling of separate sample vials is very time consuming and includes potential risk of setting the sample vials in incorrect order into the sample racks. The sample changing mechanism of such an instrument is also rather complicated, because the vial must be removed from the sample rack and must be positioned into a light tight radiation detection chamber, and after counting it must be returned back into the sample rack.
In addition to the above mentioned conventional liquid scintillation counters, one special purpose liquid scintillation counter exists, namely 1205 Betaplate, which is manufactured by Wallac Oy, Finland. This instrument is designed to count liquid scintillation samples directly from a filter mat, which is sealed into a plastic bag with a small amount of scintillation liquid. On the same filter mat there can be up to 96 samples, and six samples are counted at a time.